Ethanol is metabolized by alcohol dehydrogenase to acetaldehyde, a known toxic agent that can form adducts on macromolecules. The levels of acetaldehyde and other aldehydes increase under oxidative stress, and the increase in aldehydic load is associated with a number of common human pathologies. Relevant to this proposal, increased aldehydic load contributes to neurodegeneration. A major defense from acetaldehyde and from other aldehydes that we generate or are exposed to from the environment is the mitochondrial matrix enzyme, aldehyde dehydrogenase 2 (ALDH2). Ten years ago, our research (supported by this grant) demonstrated a critical cytoprotective role for ALDH2: direct activation with a small molecule that we discovered, Alda-1, reduces oxidative damage in a number of cell and animal models of human diseases. A common human inactivating point mutation in ALDH2 (ALDH2*2), present in ~560 million East Asians, increases the cell injury and cell death by aldehydic load induced by high levels of ethanol or by oxidative stress, and Alda-1 treatment reduces this injury. Because ALDH2*2 mutation is so common, we propose the HYPOTHESIS that additional ALDH2 deficiencies may exist in significantly large numbers in populations other than East Asians. Supported by our preliminary data, in AIM 1 we plan to identify and characterize new common ALDH2 variants, determine the effect of these variants on ethanol-induced acetaldehyde metabolism in human cells and identify new small molecules (ALDH2 activators; Aldas) that correct these newly identified inactive variants. Mounting evidence connects aldehydic load and neurodegenerative diseases, such as Alzheimer?s disease (AD). There is also a significant increased risk for AD among carriers of ALDH2*2 genotype. Because mitochondrial dysfunction contributes to neurodegeneration and aldehydes cause mitochondrial dysfunction, and because there is a correlation between frequent alcohol consumption, increased risk of dementia and a potential role for acetaldehyde in neurodegeneration, we plan to test our second HYPOTHESIS that inactivating variants of ALDH2 and the higher acetaldehyde levels following ethanol consumption contribute to mitochondrial dysfunction and thus to neurodegeneration. In AIM 2, we will characterize new ALDH2-inactive variants and their effect on mitochondrial structure and function in the presence of ethanol in cultured neuronal cells, in AD patient-derived cells, and in an AD mouse model expressing inactivating ALDH2 variants, in the presence or absence of chronic exposure to moderate levels of ethanol. Over 80% of the population in the US consumes alcoholic beverages. As ~1-2% of people over the age of 65 and ~30% of people over 80 develop AD, the possibility that ethanol consumption contributes to the progression of the disease in the general population and in patients deficient in ALDH2 activity, and the identification of a potential therapeutic intervention, are the subjects of this proposal.